In a film-forming apparatus for forming a thin film according to, for instance, the sputtering technique, the vacuum deposition technique, the ion-plating technique, or the CVD technique, a film of a metal or a metal compound, as a film-forming material, is inevitably adhered to a constituent member for a film-forming chamber, which is positioned within the film-forming apparatus during the film-forming process. As such constituent members for a film-forming chamber, there can be listed, for instance, an adhesion-preventive plate for inhibiting the adhesion of any film on the inner portions of a vacuum chamber other than a substrate, a shutter, a mask used for forming such a film only on the desired area on the substrate and a tray for conveying the substrate. A film having the same composition as that of the intended thin film (a thin film to be formed on a substrate) is also deposited on or adhered to these members during the film-forming process. In this respect, it is the usual practice that these members are repeatedly used after the removal of the film adhered thereto.
The film inevitably adhered to these constituent members for a film-forming chamber is thickened in proportion to the length of the working time of the film-forming process. Such an adhered film is peeled off, in the form of particles, from the constituent members for a film-forming chamber due to the action of the internal stress of the adhered film or the stress accumulated in the film through the repeated thermal hysteresis, and adhered to the substrate and this would accordingly result in the formation of a film having various defects. For this reason, it is the common practice that the constituent members for a film-forming chamber are subjected to the following cycle, at regular intervals; the removal or dismantlement thereof from the film-forming apparatus at a stage in which the adhered film is not yet peeled off, the washing thereof to remove the film adhered thereto, the subjection thereof to a surface-finishing treatment and the subsequent reuse thereof.
When using a valuable metal such as Al, Mo, Co, W, Pd, Nd, In, Ti, Re, Ta, Au, Pt, Se and Al, as a film-forming material, there has been desired for the establishment of a processing technique for the recovery of metals which do not take part in the formation of the film thereof on the surface of a substrate and are adhered to the constituent members other than the substrate and for the development of a technique for making the members reusable.
For instance, in the case of the adhesion-preventive plate used for inhibiting the adhesion of any film-forming material onto, for instance, the inner wall of the film-forming apparatus and the surface of a variety of such constituent members for a film-forming chamber, other than the surface of a substrate, the deposit formed during the film-forming process is, in the existing circumstances, peeled off from the foregoing members and/or the inner wall, for the reuse thereof. Currently used as such a method for the peeling off of this deposit include, for instance, the sandblasting technique, the wet etching technique which makes use of an acid or an alkali and the peeling technique which uses the hydrogen embrittlement by the action of, for instance, hydrogen peroxide and even the peeling method which makes use of the electrolysis thereof. In this case, when implementing the treatment for peeling off of the deposit, the adhesion-preventive plate is damaged in a treating liquid in no small quantities and therefore, the adhesion-preventive plate would be limited in the number of reusable times. For this reason, there has been desired for the development of a film-peeling technique which can reduce the occurrence of any damage of the adhesion-preventive plate as low as possible.
In this respect, however, if the concentration of the peeled deposit present in the blasting waste generated during the foregoing sandblasting technique and in the waste liquor generated in the treatment with an agent such as an acid treatment or an alkali treatment is low, the cost required for the recovery of the valuable metals is correspondingly quite high and accordingly, this method is not profitable. In such case, the deposit thus peeled off is accordingly handled as waste, under the present conditions.
In the foregoing treatment with an agent, not only the cost for the agent per se is high, but also the cost required for the post-treatment of the used liquid containing such an agent is high and further the occurrence of any environmental pollution should be prevented. For this reason, there has been desired for the reduction of the amount of the foregoing agent to be used as low as possible. In addition, when carrying out the foregoing treatment with an agent, the film-forming material peeled off from the adhesion-preventive plate would be converted into other new chemical substances and therefore, the cost required for the recovery of only the film-forming material from the peeled deposit would further be piled up. Accordingly, the materials to be recovered are only the film-forming materials whose unit price is balanced with the recovery cost, in the existing circumstances.
In addition to the method for peeling off of the deposit, as has been discussed above, there has been known a technique for recovering valuable metals which comprises the steps of implementing a film-forming process in an apparatus provided with constituent members covered with an Al film consisting of a water-reactive Al composite material having such characteristic properties that it can undergo a reaction in a moisture-containing atmosphere and can thus be converted into substances soluble or active in water; peeling off and separating the film adhered to the Al film, during the film-forming process, through the reaction and/or dissolution of the Al film; and then recovering the valuable metals included in the film-forming material present in the adhered film thus peeled off (see, for instance, Patent Document 1 specified below). In this water-reactive Al composite material, the surface of a small or fine lump composed of Al crystalline grains is covered with a film of In and/or Si.